The present invention relates to a photomask, a manufacturing apparatus and method of semiconductor device using the same, and a photomask feature layout method, and particularly relates to a photomask having a sub-feature for increasing a depth of focus of an exposure feature, a manufacturing apparatus and a method of a semiconductor device using the same, and a photomask feature layout method.
The progress of semiconductor manufacturing technology has brought about increasingly miniaturized circuit features that are formed on a substrate through the lithography process. In the lithography process, a main feature with a shape and dimension in accordance with the circuit feature is formed on a photomask. In addition, a photoresist layer is coated on the surface of the substrate, light is irradiated to the photoresist layer via the photomask from a light source to form an exposure feature on the photoresist layer. The photoresist layer is then developed to remove unnecessary parts, and the substrate is etched to form a circuit feature on the surface of the substrate.
In order to form a more miniature circuit feature, it is necessary to form a high-resolution exposure feature having a sufficient depth of focus (DOF). However, light passing through a main feature arranged in an isolated manner cannot particularly provide a sufficient depth of focus due to its limited wavelength. Therefore, a method is known in which, in addition to the main feature, a sub-feature which acts as the Sub-Resolution Assist Feature (SRAF) is laid near the main feature to increase the resolution. The sub-feature is formed on the surface of the substrate with a dimension smaller than the resolution limit.
In patent document 1 (Japanese Patent Laid-Open No. 2009-229669), for example, a square or rectangular sub-feature is laid along each side of a square or rectangular main feature. In patent document 2 (Japanese Patent Laid-Open No. 2005-55878) and patent document 3 (Japanese Patent Laid-Open No. 2004-272228), a number of sub-features are arranged at a constant pitch around a plurality of main features arranged at a constant pitch.
With patent document 1, however, since no sub-feature is laid on a part not facing the side of the main feature, the size of the depth of focus has not been sufficiently satisfactory. Additionally, with patent documents 2 and 3, it has been impossible to lay a sub-feature if a plurality of main features is not arranged in X- and Y-directions at a constant pitch.
Accordingly, it is a main object of the present invention to provide a photomask which can provide a large depth of focus even if four main features are annularly arranged at random, a manufacturing apparatus and method of a semiconductor device using the same, and a photomask feature layout method.